Advances in semiconductor processing and logic design have permitted an increase in the amount of logic that may be present on integrated circuit devices. As a result, computer system configurations have evolved from a single or multiple integrated circuits in a system to multiple hardware threads, multiple cores, multiple devices, and/or complete systems on individual integrated circuits. Additionally, as the density of integrated circuits has grown, the power requirements for computing systems (from embedded systems to servers) have also escalated. Furthermore, software inefficiencies, and its requirements of hardware, have also caused an increase in computing device energy consumption. In fact, some studies indicate that computing devices consume a sizeable percentage of the entire electricity supply for a country, such as the United States of America. As a result, there is a vital need for energy efficiency and conservation associated with integrated circuits. These needs will increase as servers, desktop computers, notebooks, ultrabooks, tablets, mobile phones, processors, embedded systems, etc. become even more prevalent (from inclusion in the typical computer, automobiles, and televisions to biotechnology).
Power management for integrated circuits such as processors (used in both server and client systems) depends on accurate measurements of estimates of current processor power consumption. Various components of a processor may have their voltage and frequency modulated to stay within specified power limits. Since exceeding a power constraint is undesirable, processors are tuned to always stay under the power limit. Errors in power measurement are accounted for as a guardband, resulting in reduced power being available for processor performance.
Consider a processor that has a 100 watt (W) power limit, also referred to as a thermal design power (TDP), and a +/−5% error in power measurement. Since the processor must stay below its power limit, it caps power when a power consumption of 95 W is measured, making 5 W unavailable for use because it is reserved as a guardband. The size of this guardband is directly proportional to the amount of the error. These guardbands thus reduce available power. Further, inaccuracies of different types of power monitors can vary at low and high loads.